A thermal cycle of a heat engine that employs a quantity of gas as an operating medium can be described by reference to a pressure-volume (P-V) diagram. The net energy delivered from one thermal cycle is the area of the loop swept out by the operating path in the P-V plane. In the course of each cycle, energy is delivered by the engine for part of the cycle, and is absorbed by the engine for the remainder of the cycle. For some parts of some cycles, energy is neither stored nor delivered.
By necessity, part of the system used for extracting a net positive average power output must include a device for storing and returning energy out of and into the heat engine, on a cyclic basis. In conventional heat engines, this cyclic energy storage is accomplished by mechanical means, for example via the rotational inertia of a crankshaft with flywheel attached.
By contrast with such conventional heat engines that use mechanical means for cyclic energy storage, U.S. Pat. No. 7,690,199 B2 of Wood, entitled “System and Method for Electrically-Coupled Thermal Cycle,” the disclosure of which is incorporated herein by reference in its entirety, describes an electrically-coupled thermal cycle.
There is an ongoing need to produce fuel efficient engines, vehicles and thermal cycles.